Dynamic transistor gate overdrive for input/output (I/O) drivers and level shifters

ABSTRACT

An apparatus for generating an output voltage signal based on an input voltage signal. The apparatus includes a first field effect transistor (FET) including a first gate configured to receive a first gate voltage based on the input voltage signal; a second (FET) including a second gate configured to receive a second gate voltage based on the input voltage signal, wherein the first and second FETs are coupled in series between a first voltage rail and a second voltage rail, and wherein the output voltage signal is produced at an output node between the first and second FETs; and a gate overdrive circuit configured to temporarily reduce the first gate voltage during a portion of a transition of the output voltage signal from a logic low level to a logic high level.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No. 16/653,391, filed on Oct. 15, 2019, which is incorporated herein by reference.

FIELD

Aspects of the present disclosure relate generally to input/output (I/O) drivers and level shifters, and in particular, to dynamic or temporary transistor gate overdrive for I/O drivers and level shifters.

DESCRIPTION OF RELATED ART

An input/output (I/O) driver typically receives an input voltage in a first voltage domain (e.g., a voltage domain suitable for digital signal processing in an integrated circuit (IC), such as a system on chip (SOC)) and generates an output voltage in a second voltage domain (e.g., a voltage domain suitable for signal transmission via metallization traces on a printed circuit board (PCB)). As an example, the input voltage may swing between a logic low level of 0 Volt (V) and a logic high level of +0.9V according to the first voltage domain, and the output voltage may swing between a logic low level of 0V and a high logic level of +3.05V according to the second voltage domain.

A level shifter may perform a similar function as discussed above with reference to the I/O driver, but may not be used to generate an output voltage for transmission via metallization traces on a PCB. As an example, a level shifter may perform an intermediate voltage level shift within an I/O driver or in other applications. For instance, a level shifter may level shift the input voltage from the first voltage domain (e.g., 0-0.9V) to an intermediate voltage domain (e.g., 0-1.8V).

In both I/O drivers and level shifters, it is often desirable to use relatively small transistors (e.g., field effect transistors (FETs)) so that they can operate at desirable high frequencies, and occupy a relatively small footprint of IC, among other benefits.

SUMMARY

The following presents a simplified summary of one or more implementations in order to provide a basic understanding of such implementations. This summary is not an extensive overview of all contemplated implementations, and is intended to neither identify key or critical elements of all implementations nor delineate the scope of any or all implementations. Its sole purpose is to present some concepts of one or more implementations in a simplified form as a prelude to the more detailed description that is presented later.

Another aspect of the disclosure relates to an apparatus for generating an output voltage signal based on an input voltage signal. The apparatus includes a first field effect transistor (FET) including a first gate configured to receive a first gate voltage based on the input voltage signal; a second (FET) including a second gate configured to receive a second gate voltage based on the input voltage signal, wherein the first and second FETs are coupled in series between a first voltage rail and a second voltage rail, and wherein the output voltage signal is produced at an output node between the first and second FETs; and a gate overdrive circuit configured to temporarily reduce the first gate voltage during a first portion of a transition of the output voltage signal from a logic low level to a logic high level.

An aspect of the disclosure relates to a method of generating an output voltage signal based on an input voltage signal. The method includes applying a first gate voltage to a first gate of a first field effect transistor (FET) based on the input voltage signal; applying a second gate voltage to a second gate of a second (FET) based on the input voltage signal, wherein the first and second FETs are coupled in series between a first voltage rail and a second voltage rail, and wherein the output voltage signal is produced at an output node between the first and second FETs; and temporarily reducing the first gate voltage during a first portion of a transition of the output voltage signal from a logic low level to a logic high level.

Another aspect of the disclosure relates to an apparatus for generating an output voltage signal based on an input voltage signal. The apparatus includes means for applying a first gate voltage to a first gate of a first field effect transistor (FET) based on the input voltage signal; means for applying a second gate voltage to a second gate of a second (FET) based on the input voltage signal, wherein the first and second FETs are coupled in series between a first voltage rail and a second voltage rail, and wherein the output voltage signal is produced at an output node between the first and second FETs; and means for temporarily reducing the first gate voltage during a portion of a transition of the output voltage signal from a logic low level to a logic high level.

To the accomplishment of the foregoing and related ends, the one or more implementations include the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative aspects of the one or more implementations. These aspects are indicative, however, of but a few of the various ways in which the principles of various implementations may be employed and implementations in the description are intended to include all such aspects and their equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a schematic diagram of an exemplary input/output (I/O) driver in accordance with an aspect of the disclosure.

FIG. 1B illustrates a timing diagram associated with an exemplary operation of the I/O driver of FIG. 1A in accordance with another aspect of the disclosure.

FIG. 2A illustrates a schematic diagram of another exemplary input/output (I/O) driver in accordance with another aspect of the disclosure.

FIG. 2B illustrates a timing diagram associated with an exemplary operation of the I/O driver of FIG. 2A in accordance with another aspect of the disclosure.

FIG. 3 illustrates a schematic diagram of an exemplary gate overdrive (enable) circuit in accordance with another aspect of the disclosure.

FIG. 4 illustrates a schematic diagram of an exemplary gate overdrive (voltage generating) circuit in accordance with another aspect of the disclosure.

FIG. 5A illustrates a schematic diagram of an exemplary level shifter in accordance with another aspect of the disclosure.

FIG. 5B illustrates a timing diagram associated with an exemplary operation of the level shifter of FIG. 5A in accordance with another aspect of the disclosure.

FIG. 6 illustrates a schematic diagram of an exemplary gate overdrive circuit for a level shifter in accordance with another aspect of the disclosure.

FIG. 7 illustrates a schematic diagram of another exemplary gate overdrive circuit for a level shifter in accordance with another aspect of the disclosure.

FIG. 8 illustrates a schematic diagram of another exemplary gate overdrive circuit for a level shifter in accordance with another aspect of the disclosure.

FIG. 9 illustrates a schematic diagram of another exemplary gate overdrive circuit for a level shifter in accordance with another aspect of the disclosure.

FIG. 10 illustrates a flow diagram of an exemplary method of generating an output voltage based on an input voltage in accordance with another aspect of the disclosure.

FIG. 11 illustrates a block diagram of an exemplary wireless device in accordance with another aspect of the disclosure.

DETAILED DESCRIPTION

The detailed description set forth below, in connection with the appended drawings, is intended as a description of various configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of the various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. In some instances, well-known structures and components are shown in block diagram form in order to avoid obscuring such concepts.

FIG. 1A illustrates a schematic diagram of an exemplary input/output (I/O) driver 100 in accordance with an aspect of the disclosure. The I/O driver 100 is configured to receive an input voltage signal V_(in), and generate therefrom an output voltage signal V_(out). The output voltage signal V_(out) may be applied across a load.

The input voltage signal V_(in) may be in a first voltage domain vddcx, which may pertain to the voltage domain suitable for digital signal processing in an integrated circuit (IC), such as a silicon on chip (SOC). In the first voltage domain vddcx, the input voltage signal V_(in) may swing between a first upper supply voltage vddcx and a lower supply voltage (e.g., GND or 0 Volt (V)). As an example, the first upper supply voltage vddcx may be +0.9V.

The output voltage signal V_(out) may be in a second voltage domain vddpx, which may pertain to the voltage domain suitable for digital signal transmission via metallization traces of a printed circuit board (PCB) upon which the IC or SOC is mounted. In the second voltage domain vddpx, the output voltage signal V_(out) may swing between a second upper supply voltage vddpx and the lower supply voltage 0V. As an example, the second upper supply voltage vddpx may be +3.05V, which is higher than the first upper supply voltage Vddcx of +0.9V.

More specifically, the I/O driver 100 includes a first level shifter 110, a second level shifter 120, a buffer 130, and an output circuit 140. The output circuit 140, in turn, includes a first p-channel metal oxide semiconductor (PMOS) field effect transistor (FET) M_(P1), a second PMOS FET M_(P2), a first n-channel metal oxide semiconductor (NMOS) FET M_(N1), and a second NMOS FET M_(N2). The first and second PMOS FETs M_(P1) and M_(P2) and the first and second NMOS FETs M_(N1) and M_(N2) are coupled in series in that order between an upper voltage rail configured to receive the second upper supply voltage vddpx and a low voltage rail configured to receive the lower supply voltage (e.g., GND or 0V). The output voltage signal V_(out) is generated at a node between the second PMOS FET M_(P2) and the first NMOS FET M_(N1).

The first level shifter 110 is configured to level shift the input voltage signal V_(in) to generate an intermediate voltage signal V_(m). The intermediate voltage signal V_(m) is in an intermediate voltage domain “vdd_1 p 8” which, for example, swings between a third upper supply voltage vdd_1 p 8 and the lower supply voltage (e.g., GND or 0V). As an example, the third upper supply voltage vddpx may be +1.8V, which is higher than the first upper supply voltage vddcx of +0.9V, but lower than the second upper supply voltage vddpx of +3.05V. To perform the specified level shift, the first level shifter 110 is coupled to a voltage rail configured to receive the first upper supply voltage vddcx, a voltage rail configured to receive the third upper supply voltage vdd_1 p 8, and a voltage rail configured to receive the lower supply voltage GND. The intermediate voltage signal V_(m) is applied to respective inputs of the second level shifter 120 and the buffer 130.

The second level shifter 120 is configured to level shift the intermediate digital signal V_(m) to generate a gate drive voltage V_(PCTL) for the PMOS FET M_(P1) of the output circuit 140. The voltage domain of the gate driver voltage V_(PCTL) swings between the second upper supply voltage vddpx and a fourth upper supply voltage “vdd_sink”. As an example, the fourth upper supply voltage vdd_sink may be +1.25V, which is higher than the first and lower supply voltages vddcx and GND of +0.9V and 0V, respectively, and lower than the second and third supply voltages vddpx and vdd_1 p 8, respectively. To perform the specified level shift, the second level shifter 120 is coupled to the voltage rail configured to receive the second upper supply voltage vddpx, the voltage rail configured to receive the third upper supply voltage vdd_1 p 8, the voltage rail configured to receive the lower supply voltage GND, and a voltage rail configured to receive a fourth supply voltage vdd_sink.

The buffer 130 is configured to buffer the intermediate digital signal V_(m) to generate a gate drive voltage V_(nctl) for the second NMOS FET M_(N2) of the output circuit 140. As the operation is buffering, the gate drive voltage V_(nctl) for the NMOS FET M_(N2) is in the same voltage domain as the intermediate voltage signal V_(m). That is, the gate drive voltage V_(nctl) swings between the third upper supply voltage vdd_1 p 8 and the lower supply voltage GND or 0V. To perform the buffering operation, the buffer 130 is coupled to the voltage rail configured to receive the third upper supply voltage vdd_1 p 8, and the voltage rail configured to receive the lower supply voltage GND.

A substantially constant bias voltage V_(pbias) is applied to the gate of the second PMOS FET M_(P2) of the output circuit 140. As an example, the bias voltage V_(pbias) may set to substantially +1.25V. Another substantially constant bias voltage V_(nbias) is applied to the gate of the second NMOS FET M_(N2) of the output circuit 140. As an example, the bias voltage V_(nbias) may set to substantially +1.8V. The bias voltages V_(pbias) and V_(nbias) are configured to protect the FETs M_(P1), M_(P2), M_(N1), and M_(N2) from voltages across any terminals of these devices which would exceed their maximum voltage reliability limit. For example, if such reliability limit is 2.0V, then the bias voltages V_(pbias) and V_(nbias) set to +1.25 and +1.8V, respectively, prevents the voltage across any terminals of these devices from exceeding 2.0V. The maximum voltage reliability limit is relatively small (e.g., 2.0V) because the FETs M_(P1), M_(P2), M_(N1), and M_(N2) may be made relatively small to allow for faster and high frequency operations.

FIG. 1B illustrates a timing diagram associated with an exemplary operation of the I/O driver 100 in accordance with another aspect of the disclosure. The x- or horizontal axis of the diagram represents time, and the y- or vertical axis represents voltages of various signals. These signals, from top to bottom, are the gate drive voltage V_(pctl) for the first PMOS FET M_(P1), the bias voltage V_(pbias) for the gate of the second PMOS FET M_(P2), the output voltage signal V_(out), the bias voltage V_(nbias) for the gate of the first NMOS FET M_(N1), and the gate drive voltage V_(nctl) for the second NMOS FET M_(N2).

The operation of the I/O driver 100 is as follows: at time to, the input voltage signal V_(in) is at a logic low level (e.g., 0V), the first level shifter 110 generates the intermediate voltage signal V_(m) also at a logic low level (e.g., 0V), the second level shifter 120 generates the gate drive voltage V_(pctl) for the first PMOS FET M_(P1) at a logic low level (e.g., +1.25V), and the buffer 130 generates the gate drive voltage V_(nctl) for the second NMOS FET M_(N2) at a logic low level (e.g., 0V).

The gate drive voltage V_(pctl) being at 1.25V causes the first PMOS FET M_(P1) to turn on as the gate-to-source voltage V_(gs) (e.g., vddpx-V_(pctl)=3.05-1.25V=1.8V) is greater than a threshold voltage V_(T) of 0.4V. The turning on of the first PMOS FET M_(P1) causes the supply voltage vddpx to be substantially applied to the source of the second PMOS FET M_(P2). Since the bias voltage V_(pbias) applied to the gate of the second PMOS FET M_(P2) is at +1.25V, the second PMOS FET M_(P2) also turns on as its gate-to-source voltage V_(gs) (e.g., vddpx-V_(pbias)=3.05-1.25V=1.8V) is greater than the threshold voltage V_(T) of 0.4V.

The gate drive voltage V_(nctl) being at 0V causes the second NMOS FET M_(N2) to turn off as the gate-to-source voltage V_(gs) (e.g., V_(nctl)-GND=0V-V=0V) is less than a threshold voltage V_(T) of 0.4V. Since the second NMOS FET M_(N2) is off, no current path exists between the output voltage node and the lower voltage rail GND; thus, the first NMOS FET M_(N1) is also turned off. In this configuration, the output voltage signal V_(out) is at a logic high level at substantially vddpx (e.g., +3.05V). Thus, in this example, the I/O driver 100 inverts the logic state of the input voltage signal V_(in) to generate the output voltage signal V_(out).

At time t₁, the input voltage signal V_(in) transitions to a logic high level (e.g., +0.9V), the first level shifter 110 generates the intermediate voltage signal V_(m) also at a logic high level (e.g., +1.8V), the second level shifter 120 generates the gate drive voltage V_(pctl) for the first PMOS FET M_(P1) at a logic high level (e.g., +3.05V), and the buffer 130 generates the gate drive voltage V_(nctl) for the second NMOS FET M_(N2) at a logic high level (e.g., +1.8V).

The gate drive voltage V_(pctl) being at +3.05V causes the first PMOS FET M_(P1) to turn off as the gate-to-source voltage V_(gs) (e.g., vddpx-V_(pctl)=3.05-3.05V=0V) is less than the threshold voltage V_(T) of 0.4V. The turning off of the first PMOS FET M_(P1) prevents the supply voltage vddpx from being applied to the source of the second PMOS FET M_(P2). Thus, the second PMOS FET M_(P2) is also off as there is substantially no current flowing through the second PMOS FET M_(P2).

The gate drive voltage V_(nctl) being at +1.8V (greater than half vddpx) causes the second NMOS FET M_(N2) to turn on as the gate-to-source voltage V_(gs) (e.g. V_(nctl)-GND=1.8V-0V=1.8V) is greater than the threshold voltage V_(T) of 0.4V. Since the second NMOS FET M_(N2) is on, the ground potential is substantially applied to the source of the first NMOS FET M_(N1). Since the bias voltage V_(nbias) applied to the gate of the first NMOS FET M_(N1) is at +1.8V, the first NMOS FET M_(N1) also turns on as its gate-to-source voltage V_(gs) (e.g., V_(nbias)-GND=1.8V-0V=1.8V) is greater than the threshold voltage V_(T) of 0.4V. In this configuration, the output voltage signal V_(out) decreases from vddpx (e.g., 3.05V) towards GND (0V) as the load typically has capacitive component which discharges when GND is applied to the output node. As illustrated, at time t₂, the output signal V_(out) settles at substantially 0V.

At time t₃, the input voltage signal V_(in) transitions back to a logic low level (e.g., 0V), in response: the first level shifter 110 generates the intermediate voltage signal V_(m) also at a logic low level (e.g., 0V), the second level shifter 120 generates the gate drive voltage V_(pctl) for the first PMOS FET M_(P1) at a logic low level (e.g., +1.25V), and the buffer 130 generates the gate drive voltage V_(nctl) for the second NMOS FET M_(N2) at a logic low level (e.g., 0V).

The gate drive voltage V_(pctl) being at 1.25V causes the first PMOS FET M_(P1) to turn on as the gate-to-source voltage V_(gs) (e.g., vddpx-V_(pctl)=3.05-1.25V=1.8V) is greater than the threshold voltage V_(T) of 0.4V. The turning on of the first PMOS FET M_(P1) causes the supply voltage vddpx to be substantially applied to the source of the second PMOS FET M_(P2). Since the bias voltage V_(pbias) applied to the gate of the second PMOS FET M_(P2) is at +1.25V, the second PMOS FET M_(P2) also turns on as its gate-to-source voltage V_(gs) (e.g., vddpx-V_(pbias)=3.05-1.25V=1.8V) is greater than the threshold voltage V_(T) of 0.4V.

The gate drive voltage V_(nctl) being at 0V causes the second NMOS FET M_(N2) to turn off as the gate-to-source voltage V_(gs) (e.g., V_(nctl)-GND=0V-0V=0V) is less than the threshold voltage V_(T) of 0.4V. Since the second NMOS FET M_(N2) is off, no current path exists between the output voltage node and the lower voltage rail GND; thus, the first NMOS FET M_(N1) is also turned off. In this configuration, the output voltage signal V_(out) rises from GND towards vddpx (e.g., +3.05V) by vddpx being substantially applied across the capacitive load. As illustrated, at time t₅, the output voltage signal V_(out) settles at substantially +3.05V.

There are several drawbacks with the I/O driver 100. One drawback stems from the amount of power supplies required by the I/O driver 100. For example, as discussed, power supplies are needed to generate supply voltages vddcx, vdd_1 p 8, vdd_sink, and vddpx. In this example, two power supplies vdd_sink and vdd_1 p 8 are needed to support overdrive of the gate voltage of the first PMOS FET M_(P1) and the second NMOS FET M_(N2), respectively. However, this may be undesirable because the relatively large number of power supplies needed requires substantial IC footprint to implement including additional pads, metal routings, vias, filtering capacitors, etc.

Another solution is to use a single power supply, for example, vdd_1 p 8, for both the gate drive voltage to turn on the first PMOS FET M_(P1) and the second NMOS FET M_(N2). However, the supply voltage vdd_1 p 8 of, for example, +1.8V may not be enough to sufficiently to turn on the first PMOS FET M_(P1) at a desired size for this device. For example, in a worst case scenario, the supply voltage vddpx may be as low as +2.7V, the logic high level of the gate drive voltage V_(pctl) may be as high as +1.95V, and the threshold voltage V_(T) of the first PMOS FET M_(P1) may be as high as 0.6V. Thus, the gate-to-source voltage V_(gs) of the first PMOS FET M_(P1), being at 0.8V (2.7V-1.95V), is about 0.2V higher than the threshold voltage V_(T) of 0.6V. Accordingly, the V_(gs) in the worst case scenario may not be sufficient to properly turn on the first PMOS FET M_(P1) for effective operation of the I/O driver 100.

To combat this, the first PMOS FET M_(P1) may be made to be, for example, four (4) times larger to sufficiently turn on with a V_(gs) of 0.2V above the threshold voltage V_(T). But the increase in FET size generally has the undesirable consequence of requiring a larger IC footprint to implement the I/O driver 100, and may adversely affect the high frequency performance of the driver.

FIG. 2A illustrates a schematic diagram of another exemplary input/output (I/O) driver 200 in accordance with another aspect of the disclosure. In summary, the I/O driver 200 is similar to that of I/O driver 100, but eliminates the supply voltage vdd_sink, and includes a gate overdrive circuit to dynamically or temporarily reduce the gate drive voltage V_(pctl) for the first PMOS FET M_(P1) below its logic low level, and dynamically or temporarily reduce the gate bias voltage V_(pbias) for the second PMOS FET M_(P2) in response to a negative transition of the gate drive signal V_(nctl) for the second NMOS FET M_(N2). When the output voltage signal V_(out) rises to a certain threshold level, the gate overdrive circuit returns the gate drive voltage V_(pctl) to the logic low level and the gate bias voltage V_(pbias) to its non-overdrive voltage level. In other words, the gate overdrive circuit can temporarily reduce the gate drive voltage V_(pctl) for the first PMOS FET M_(P1) below its logic low level during a first portion of the transition of the output voltage signal V_(out), and then raise the gate drive voltage V_(pctl) during a second portion of the transition of the output voltage signal V_(out).

In particular, the I/O driver 200 includes a first level shifter 210, a second level shifter 220, a buffer 230, an output circuit 240, a gate overdrive (enable) circuit 250, and an inverter 260. The output circuit 240 is similar to output circuit 140 previously discussed, including first and second PMOS FETs M_(P1) and M_(P2) and first and second NMOS FETs M_(N1) and M_(N2) coupled in series in that order between the vddpx voltage rail and the GND voltage rail. An output voltage signal V_(out) is generated at a node between the second PMOS FET M_(P1) and the first NMOS FET M_(N1). The output voltage signal V_(out) may be provided across a load.

The first level shifter 210 operates similar to the first level shifter 110 previously discussed in detail. That is, the first level shifter 210 level shifts an input voltage signal V_(in) in the first voltage domain vddcx to generate the intermediate voltage signal V_(m) in the third voltage domain vdd_1 p 8. As discussed, the first level shifter 210 is coupled to the vddcx, vdd_1 p 8, and GND voltage rails. The intermediate voltage signal V_(m) is provided to the second level shifter 220 and the buffer 230.

The buffer 230 operates similar to the buffer 130 previously discussed in detail. That is, the buffer 230 buffers the intermediate voltage signal V_(m) to generate the gate drive voltage V_(nctl) for the second NMOS FET M_(N2). As discussed, the buffer 230 is coupled to the vdd_1 p 8 and GND voltage rails.

The second level shifter 220 is different than the first level shifter 110. The second level shifter 220 level shifts the intermediate voltage signal V_(m) to generate a gate drive voltage V_(pctl) for the first PMOS FET M_(P1) that swings between vddpx and vdd_1 p 8 during no gate overdrive. The second level shifter 220 is also responsive to a pulse enable signal V_(pulse_en) to reduce the gate drive signal V_(pctl) below the logic low level vdd_1 p 8 to a first overdrive voltage V_(ovd1) in response to an assertion of the pulse enable signal V_(pulse_en). The second level shifter 220 is also responsive to the pulse enable signal V_(pulse_en) to raise the gate control voltage V_(pctl) from the first overdrive voltage V_(ovd1) to the logic low level vdd_1 p 8 in response to deassertion of the pulse enable signal V_(pulse_en). In this case, the second level shifter 220 is coupled to the vdd_1 p 8, vddpx, and GND voltage rails, as the voltage rail vdd_sink is not needed in I/O driver 200.

The gate overdrive (enable) circuit 250 is configured to generate the pulse enable signal V_(pulse_en) based on the gate drive voltage V_(nctl) for the second NMOS FET M_(N2) and the output voltage signal V_(out). For example, the gate overdrive (enable) circuit 250 is configured to assert the pulse enable signal V_(pulse_en) in response to the negative (falling) transition of the gate drive voltage V_(nctl) for the second NMOS FET M_(N2). The negative transition of the gate drive voltage V_(nctl) initiates the transition of the output voltage signal V_(out) from a logic low level (e.g., 0V) to a logic high level (e.g., +3.05V). When the output voltage signal V_(out) reaches a certain level during its transition towards the logic high level, the gate overdrive (enable) circuit 250 deasserts the pulse enable signal V_(pulse_en).

Thus, the gate drive voltage V_(pctl) is dynamically or temporarily reduced below its logic low level to drive the first PMOS FET M_(P1) harder to assist the transition of the output voltage signal V_(out) to substantially vddpx. When the output voltage signal V_(out) has risen to a certain level above GND (and below vddpx), the gate drive voltage V_(pctl) is returned to the logic low level so that the first PMOS FET M_(P1) is driven normally for the remaining portion of the transition of the output voltage signal V_(out) towards substantially vddpx.

The pulse enable signal V_(pulse_en) is inverted by the inverter 260 to generate the bias voltage V_(pbias) for the second PMOS FET M_(P2). Thus, when the pulse enable signal V_(pulse_en) is deasserted at a logic low level of 0V, the inverter 260 generates the bias voltage V_(pbias) at vdd_1 p 8 (e.g., +1.8V). When the pulse enable signal V_(pulse_en) is asserted at a logic high level of vdd_1 p 8 (e.g., +1.8V) to cause the level shifter 220 to generate the gate drive voltage V_(pctl) at the first overdrive level V_(ovd1), the inverter 260 inverts the logic high level of vdd_1 p 8 (e.g., +1.8V) to generate the bias voltage V_(pbias) at a second overdrive voltage level V_(ovd2) (e.g., 0V). The overdrive gate voltages V_(ovd1) and V_(ovd2) applied to the gates of the first and second PMOS FETs M_(P1) and M_(P2) substantially coincidental assists the transition of the output voltage signal V_(out) from GND to vddpx. When the output voltage signal V_(out) has risen to a certain level during its transition towards vddpx, the gate overdrive (enable) circuit 250 deasserts the pulse enable signal V_(pulse_en) to return V_(pctl) and V_(pbias) to vdd_1 p 8 (non-overdrive level) for the remaining portion of the transition of the output voltage signal V_(out) towards vddpx.

The operation of the first and second NMOS FETs M_(N1) and M_(N2) is similar to the operation of the same FETs in I/O driver 100, as previously discussed in detail.

FIG. 2B illustrates a timing diagram associated with an exemplary operation of the I/O driver 200 in accordance with another aspect of the disclosure. Similar to the timing diagram of FIG. 1B, the x- or horizontal axis of the diagram represents time, and the y- or vertical axis represents voltages of various signals. These signals, from top to bottom, are the gate drive voltage V_(pctl) for the first PMOS FET M_(P1), the bias voltage V_(pbias) for the gate of the second PMOS FET M_(P2), the output voltage signal V_(out), the bias voltage V_(nbias) for the gate of the first NMOS FET M_(N1), and the gate drive voltage V_(nctl) for the second NMOS FET M_(N2).

The operation of the I/O driver 200 is as follows: at time to, the input digital signal V_(in) is at a logic low level (e.g., 0V), the first level shifter 210 generates the intermediate voltage signal V_(m) at a logic low level (e.g., 0V), the second level shifter 220 generates the gate drive voltage V_(pctl) for the first PMOS FET M_(P1) at a logic low level (e.g., +1.8V), and the buffer 230 generates the gate drive voltage V_(nctl) for the second NMOS FET M_(N2) at a logic low level (e.g., 0V).

The gate drive voltage V_(pctl) being at +1.8V causes the first PMOS FET M_(P1) to turn on as the gate-to-source voltage V_(gs) (e.g., vddpx-V_(pctl)=3.05-1.8V=1.25V) is greater than the threshold voltage V_(T) of 0.4V. The turning on of the first PMOS FET M_(P1) causes the supply voltage vddpx to be substantially applied to the source of the second PMOS FET M_(P2). Since the bias voltage V_(pbias) applied to the gate of the second PMOS FET M_(P2) is at +1.8V, the second PMOS FET M_(P2) also turns on as its gate-to-source voltage V_(gs) (e.g., vddpx-V_(pbias)=3.05-1.8V=1.25V) is greater than the threshold voltage V_(T) of 0.4V.

The gate drive voltage V_(nctl) being at 0V causes the second NMOS FET M_(N2) to turn off as the gate-to-source voltage V_(gs) (e.g., V_(nctl)-GND=0V-0V=0V) is less than the threshold voltage V_(T) of 0.4V. Since the second NMOS FET M_(N2) is off, no current path exists between the output voltage node and the lower voltage rail GND; thus, the first NMOS FET M_(N1) is also turned off. In this configuration, the output voltage signal V_(out) is at a logic high level at substantially vddpx (e.g., +3.05V). Thus, in this example, the I/O driver 200 inverts the logic state of the input voltage signal V_(in) to generate the output voltage signal V_(out).

At time t₁, the input voltage signal V_(in) transitions to a logic high level (e.g., +0.9V), the first level shifter 210 generates the intermediate voltage signal V_(m) at a logic high level (e.g., +1.8V), the second level shifter 220 generates the gate drive voltage V_(pctl) for the first PMOS FET M_(P1) at a logic high level (e.g., +3.05V), and the buffer 230 generates the gate drive voltage V_(nctl) for the second NMOS FET M_(N2) at a logic high level (e.g., +1.8V).

The gate drive voltage V_(pctl) being at +3.05V causes the first PMOS FET M_(P1) to turn off as the gate-to-source voltage V_(gs) (e.g., vddpx-V_(pctl)=3.05-3.05V=0V) is less than the threshold voltage V_(T) of 0.4V. The turning off of the first PMOS FET M_(P1) prevents the supply voltage vddpx from being applied to the source of the second PMOS FET M_(P2). Thus, the second PMOS FET M_(P2) is also off as there is substantially no current flowing through the second PMOS FET M_(P2).

The gate drive voltage V_(nctl) being at +1.8V causes the second NMOS FET M_(N2) to turn on as the gate-to-source voltage V_(gs) (e.g., V_(nctl)-GND=1.8V-0V=1.8V) is greater than the threshold voltage V_(T) of 0.4V. Since the second NMOS FET M_(N2) is on, the ground potential is substantially applied to the source of the first NMOS FET M_(N1). Since the bias voltage V_(nbias) applied to the gate of the first NMOS FET M_(N1) is at +1.8V, the first NMOS FET M_(N1) also turns on as its gate-to-source voltage V_(gs) (e.g., V_(nbias)-GND=1.8V-0V=1.8V) is greater than the threshold voltage V_(T) of 0.4V. In this configuration, the output voltage signal V_(out) decreases from vddpx (e.g., 3.05V) towards GND (0V) as the load typically has capacitive component which discharges when GND is applied to the output node. As illustrated, at time t₂, the output voltage signal V_(out) settles at substantially 0V.

At time t₃, the input voltage signal Vi transitions back to a logic low level (e.g., 0V), in response: the first level shifter 210 generates the intermediate voltage signal V_(m) also at a logic low level (e.g., 0V), and the buffer 230 generates the gate drive voltage V_(nctl) for the second NMOS FET M_(N2) at a logic low level (e.g., 0V). In response to the negative transition of the gate drive voltage V_(nctl), the gate overdrive (enable) circuit 250 asserts the pulse enable signal V_(pulse_en). In response to the asserted pulse enable signal V_(pulse_en), the level shifter 220 and the inverter 260 generate the gate drive voltage V_(pctl) and the bias voltage V_(pbias) at the first and second overdrive voltages V_(ovd1) (e.g., +1.25V, less than half vddpx) and V_(ovd2) (e.g., 0V), respectively. As discussed below, the overdrive voltages V_(ovd1) and V_(ovd2) turn on the first and second PMOS FETs M_(P1) and M_(P2) significantly hard to assist the output voltage signal V_(out) in its transition from a logic low level (0V) to a logic high level (+3.05V).

More specifically, the gate drive voltage V_(pctl) being at +1.25V causes the first PMOS FET M_(P1) to turn on as the gate-to-source voltage V_(gs) (e.g., vddpx-V_(pctl)=3.05-1.25V=1.8V) is greater than the threshold voltage V_(T) of 0.4V. The turning on of the first PMOS FET M_(P1) causes the supply voltage vddpx to be substantially applied to the source of the second PMOS FET M_(P2). Since the bias voltage V_(pbias) applied to the gate of the second PMOS FET M_(P2) is at 0V, the second PMOS FET M_(P2) also turns on as its gate-to-source voltage V_(gs) (e.g., vddpx-V_(pbias)=3.05-0V=3.05V) is greater than a nominal threshold voltage V_(T) of 0.4V.

The gate drive voltage V_(nctl) being at 0V causes the second NMOS FET M_(N2) to turn off as the gate-to-source voltage V_(gs) (e.g., V_(nctl)-GND=0V-0V=0V) is less than the threshold voltage V_(T) of 0.4V. Since the second NMOS FET M_(N2) is off, no current path exists between the output voltage node and the lower voltage rail GND; thus, the first NMOS FET M_(N1) is also turned off. In this configuration, the output voltage signal V_(out) rises from GND towards vddpx (e.g., +3.05V) by vddpx charging the capacitive load.

When the output voltage signal V_(out) has risen to a certain level between 0V and +3.05V (e.g., to +0.4V) at time t₄, the gate overdrive (enable) circuit 250 deasserts the pulse enable signal V_(pulse_en). In response to the deasserted pulse enable signal V_(pulse_en), the second level shifter 220 and the inverter 260 both generate the gate drive voltage V_(Pctl) and the bias voltage V_(pbias) at +1.8V. The first and second PMOS FETs M_(P1) and M_(P2) are still turned on since their gate-to-source voltages V_(gs) are above the threshold V_(T), but not turned on as hard during the overdrive interval t₃-t₄. As the capacitive load may vary, the duration of the overdrive interval (Δt=t₄-t₃) varies with the load. At time t₅, the output voltage signal V_(out) has risen and settles at substantially vddpx (e.g., +3.05V).

An advantage of I/O driver 200 over I/O driver 100 is less power supplies are needed in I/O driver 200. For example, I/O driver 100 has power supplies for generating four (4) different supply voltages vddcx, vdd_1 p 8, vdd_sink, and vddpx. Whereas, I/O driver 200 has three (3) power supplies for generating vddcx, vdd_1 p 8, and vddpx. The fewer power supplies translates to substantial reduction in IC footprint including less numbers of pads, metal routings, vias, filtering capacitors, etc. Furthermore, the dynamic or temporary overdrive voltages V_(ovd1) and V_(ovd2) allow the first and second PMOS FETs M_(P1) and M_(P2) to sufficiently turn on even in the worst case scenario where vddpx is as low as +2.7V and the threshold voltage V_(T) is as high as 0.6V. For instance, in the case of the first PMOS FET M_(P1), the gate-to-source voltage V_(gs) in the worst case may be 1.45V (e.g., 2.7V-1.25V), which is significantly higher than the worst case threshold voltage V_(T) of 0.6V. Similarly, in the case of the second PMOS FET M_(P2), the gate-to-source voltage V_(gs) in the worst case may be 2.7V (e.g., 2.7V-0V), which is significantly higher than the worst case threshold voltage V_(T) of 0.6V. Although the voltage across the second PMOS FET M_(P2) is higher than its maximum reliability limit (e.g., 2.0V), the reliability of the second PMOS FET M_(P2) is maintained because of the short duration of the overdrive interval t₃-t₄.

FIG. 3 illustrates a schematic diagram of an exemplary gate overdrive (enable) circuit 300 in accordance with another aspect of the disclosure. The gate overdrive (enable) circuit 300 may be an exemplary detailed implementation of the gate overdrive (enable) circuit 250 previously discussed. As discussed, the gate overdrive (enable) circuit 300 is configured to assert the pulse enable signal V_(pulse_en) in response to a negative transition of the gate drive voltage V_(nctl) for the second NMOS FET M_(N2). The gate overdrive (enable) circuit 300 is also configured to deassert the pulse enable signal V_(pulse_en) in response to the output voltage signal V_(out) rising to a certain voltage level during its transition from GND to vddpx.

In particular, the gate overdrive (enable) circuit 300 includes NMOS FETs M_(N3) and M_(N4), and a NOR gate 310. The output voltage signal V_(out) is applied to the gate and source of the NMOS FETs M_(N3) and M_(N4), respectively. The supply voltage vdd_1 p 8 is applied to the source of the NMOS FET M_(N3). The drain and source of the first and second NMOS FETs M_(N3) and M_(N4) are coupled to a first input of the NOR gate 310, respectively. The gate drive voltage V_(nctl) for the second NMOS FET M_(N2) of the output circuit 240 is applied to a second input of the NOR gate 310. The NOR gate 310 is coupled to voltage rails vdd_1 p 8 and GND. The NOR gate 310 includes an output configured to generate the pulse enable signal V_(pulse_en).

In operation, with additional reference to FIG. 2B, immediately before time t₃, the gate drive voltage V_(nctl) is at a logic high level and the output voltage signal V_(out) is at 0V. The supply voltage vdd_1 p 8 being applied to the gate of the NMOS FET M_(N4) causes the FET to turn on; thereby, providing a logic low level (0V) to the first input of the NOR gate 310. The logic high level of the gate drive voltage V_(nctl) is applied to the second input of the NOR gate 310. In response to a logic zero and a logic one applied to its respective inputs, the NOR gate 310 generates the pulse enable signal V_(pulse_en) at a low logic voltage or deasserted level.

At time t₃, the gate drive voltage V_(nctl) transitions from a logic high level to a logic low level (e.g., a negative transition). Accordingly, the inputs to the NOR gate 310 are now both at low logic levels. In response, the NOR gate 310 generates the pulse enable signal V_(pulse_en) at a logic high level or asserted level. This initiates the beginning of the overdrive interval t₃-t₄, where the gate drive voltage V_(pctl) and the bias voltage V_(pbias) for the gates of the first and second PMOS FETs M_(P1) and M_(P2) are at their overdrive levels V_(ovd1) and V_(ovd2), respectively.

When the output voltage signal V_(out) rises to substantially at or above the threshold voltage V_(T) of the NMOS FET M_(N3), the NMOS FET M_(N3) turns on and applies the logic high level vdd_1 p 8 to the first input of the NOR gate 310. The logic high level vdd_1 p 8 at the source of the NMOS FET M_(N4) causes the fourth NMOS FET M_(N4) to turn off. As the inputs to the NOR gate 310 are now logic high and low, the NOR gate 310 generates the pulse enable signal V_(pulse_en) at a logic low level or deasserted level. This terminates the overdrive interval t₃-t₄. Thus, the overdrive interval t₃-t4 is commenced when the gate drive voltage V_(nctl) has a negative transition, and ends when the output voltage signal V_(out) has risen to the threshold voltage V_(T) of the NMOS FET M_(N3).

FIG. 4 illustrates a schematic diagram of an exemplary level shifter 400 in accordance with another aspect of the disclosure. The level shifter 400 may be an exemplary detailed implementation of the second level shifter 220 previously discussed. The level shifter 400 is configured to generate the gate drive voltage V_(pctl) for the first PMOS FET M_(P1) in response to the intermediate voltage signal V_(m) and the pulse enable signal V_(pulse_en). During the non-overdrive interval (when the pulse enable signal V_(pulse_en) is deasserted), the level shifter 400 is configured to generate the gate drive voltage V_(pctl) to follow the logic state of the intermediate voltage signal V_(m) (e.g., when V_(m) is at vdd_1 p 8, V_(pctl) is at vddpx, and when V_(m) is at GND, V_(pctl) is at vdd_1 p 8). During the overdrive interval (when the pulse enable signal V_(pulse_en) is deasserted), the level shifter 400 is configured to generate gate drive voltage V_(pctl) at the first overdrive voltage V_(ovd1) (e.g., +1.25V).

In particular, the level shifter 400 includes a level shifting component 410, a resistor R_(PD), an NMOS FET M_(N5), and another NMOS FET M_(N6). The level shifting component 410 is configured to receive the intermediate voltage signal V_(m) and generate the gate drive voltage V_(pctl) for the first PMOS FET M_(P1). The level shifting component 410 is coupled to the vddpx and vdd_1 p 8 voltage rails. The resistor R_(PD), NMOS FET M_(N5), and NMOS FET M_(N6) are coupled in series between the output of the level shifting component 410 and the lower voltage rail GND. The supply voltage vdd_1 p 8 is applied to the gate of the NMOS FET M_(N5) for overvoltage protection purposes. The pulse enable signal V_(pulse_en) is applied to the gate of the NMOS FET M_(N6).

In operation, when the pulse enable signal V_(pulse_en) is deasserted, the current path between the output of the level shifting component 410 and GND is blocked by the turned off NMOS FET M_(N6). Accordingly, the level shifting component 410 is configured to level shift the intermediate voltage signal V_(m) to generate the gate drive voltage V_(pctl) for the first PMOS FET M_(P1). As discussed, the intermediate voltage signal V_(m) varies between 0V (logic low) and vdd_1 p 8 (logic high), and the gate drive voltage V_(pctl) varies between vdd_1 p 8 (logic low) and vddpx (logic high).

When the pulse enable signal V_(pulse_en) is asserted during the overdrive interval, a current path exists between the output of the level shifting component 410 and GND because of the turned on NMOS FET M_(N6). During this interval, the level shifting component 410 is attempting to set the gate drive voltage V_(pctl) at the logic low level (vdd_1 p 8). The current path between the output of the level shifting component 410 and GND reduces the gate drive voltage V_(pctl) in accordance with the following relationship: V _(pctl) =vdd_1p8*(R _(PD) +R _(D5) +R _(D6))/(R _(PD) +R _(D5) +R _(D6)+Out_Imped₄₁₀) where R_(PD) is the resistance of resistor R_(PD), R_(D5) is the turned-on resistance of the NMOS FET M_(N5), R_(D6) is the turned-on resistance of the NMOS FET M_(N6), and Out_Imped₄₁₀ is the output impedance of the level shifting component 410. When the pulse enable signal V_(pulse_en) is subsequently deasserted when the output voltage signal V_(out) reaches a defined voltage level, the NMOS FET M_(N6) turns off, and the gate drive voltage V_(pctl) returns back to vdd_1 p 8.

FIG. 5A illustrates a schematic diagram of an exemplary level shifter 500 in accordance with another aspect of the disclosure. The dynamic or temporary gate overdrive is not only useful for I/O drivers, but may also be used in level shifters. The level shifter 500 is an example of a level shifter that uses dynamic or temporary gate overdrive to assist a latch (cross-coupled FETs) from changing states, as explained in more detail further herein.

In particular, the level shifter 500 includes PMOS FETs M_(P3) and M_(P4) coupled in parallel between a vddpx voltage rail and a negative output node at which a negative output signal out_n of the level shifter is produced. The PMOS FET M_(P3) includes a gate configured to receive an assist_n signal, and the fourth PMOS FET M_(P4) includes a gate configured to receive a positive output signal out_p of the level shifter 500. Accordingly, the level shifter 500 is configured to generate an output differential signal out_p/out_n.

The level shifter 500 further includes a PMOS FET M₅, an NMOS FET M_(N7), and another NMOS FET M_(N8) coupled between the negative output node and a lower voltage rail GND. The PMOS FET M_(P5) includes a gate configured to receive a gate overdrive voltage V_(gn), the NMOS FET M_(N7) includes a gate configured to receive a gate bias voltage vdd_1 p 8, and the NMOS FET M_(N8) includes a gate configured to receive a positive input voltage V_(mp) of an input differential signal.

The level shifter 500 further includes a first inverter 505 including an input configured to receive the positive output signal out_p, and an output coupled to an input of a second inverter 510. The second inverter 510 includes an output coupled to a gate of an NMOS FET M_(N9). The NMOS FET M_(N9) is coupled between the negative output node and the vdd_1 p 8 voltage rail.

The level shifter 500 includes PMOS FETs M_(P6) and M_(P7) coupled in parallel between the vddpx voltage rail and a positive output node at which the positive output signal out_p of the level shifter is produced. The PMOS FET M_(P6) includes a gate configured to receive an assist_p signal, and the PMOS FET M_(P7) includes a gate configured to receive the negative output signal out_n of the level shifter 500. The FETs M_(P4) and M_(P7) form cross-coupled transistors or a latch because the input (gate) to FET M_(P4) is generated at the output (drain) of FET M_(P7), and the input (gate) to FET M_(P7) is generated at the output (drain) of FET M_(P4).

The level shifter 500 further includes an PMOS FET M_(P8), an NMOS FET M_(N10), and an NMOS FET M_(N11) coupled between the positive output node and the lower voltage rail GND. The PMOS FET M_(P8) includes a gate configured to receive a gate overdrive voltage V_(gp), the NMOS FET M_(N10) includes a gate configured to receive a gate bias voltage vdd_1 p 8, and the NMOS FET M_(N11) includes a gate configured to receive a negative input voltage V_(mn) of the input differential signal.

The level shifter 500 further includes a third inverter 515 including an input configured to receive the negative output signal out_n, and an output coupled to an input of a fourth inverter 520. The fourth inverter 520 includes an output coupled to a gate of an NMOS FET M_(N12). The NMOS FET M_(N12) is coupled between the positive output node and the vdd_1 p 8 voltage rail.

Additionally, the level shifter 500 includes an assist_n generator 530 configured to generate the assist_n signal for the gate of the PMOS FET M_(P3). The level shifter 500 further includes a V_(gn) generator 540 configured to generate the gate overdrive signal V_(gn) for the gate of the PMOS FET M_(P5). The level shifter 500 also includes an assist_p generator 550 configured to generate the assist_p signal for the gate of the PMOS FET M_(P6). The level shifter 500 further includes a V_(gp) generator 560 configured to generate the gate overdrive signal V_(gp) for the gate of the PMOS FET M_(P8).

FIG. 5B illustrates a timing diagram associated with an exemplary operation of the level shifter 500 in accordance with another aspect of the disclosure. The x- or horizontal axis of the diagram represents time, and the y- or vertical axis represents voltages of various signals. These signals, from top to bottom, are the positive input signal V_(mp), the assist_n signal for the gate of the PMOS FET M_(P3), the gate bias voltage V_(gn) for the gate of the PMOS FET M_(P5), the negative input signal V_(mn), the assist_p signal for the gate of the PMOS FET M_(P6), the gate bias voltage V_(gp) for the gate of the PMOS FET M_(P8), the positive output signal out_p, and the negative output signal out_n.

At time t₀, the positive input signal V_(mp) is at a logic low level at GND (0V), the assist_n is at a non-overdrive voltage level vddpx (e.g., +3.05V), the gate voltage V_(gn) is at a non-overdrive voltage level at vdd_1 p 8 (e.g., +1.8V), the negative input signal V_(mn) is at a logic high level at vdd_1 p 8 (e.g., +1.8V), the assist_p is at a non-overdrive voltage level at vddpx (e.g., _3.05V), the gate bias voltage V_(gp) is at a non-overdrive voltage level at vdd_1 p 8 (e.g., +1.8V), the positive output signal out_p is at a logic low level at vdd_1 p 8 (e.g., +1.8V), and the negative output signal out_n is at a logic high level at vddpx (e.g., +3.05V).

In this configuration, with regard to the left-hand or out_n side of the level shifter 500: the PMOS FET M_(P4) is turned on because the positive output signal out_p at the gate of M_(P4) is at a logic low level at vdd_1 p 8 (e.g., +1.8V); the PMOS FET M_(P3) is turned off as the assist_n signal at the gate of M_(P3) is at the non-overdrive voltage level of vddpx (e.g., +3.05V); the PMOS FET M_(P5) is turned on since the non-overdrive voltage level of vdd_1 p 8 (e.g., +1.8V) is at the gate of M_(P5); the NMOS FETs M_(N7) and M_(N8) are turned off since the positive input voltage at the gate of M_(N8) is at a logic low level (e.g., 0V); and the NMOS FET M_(N9) is turned off since the positive output voltage out_p at the gate of M_(N9) is at a logic low level at vdd_1 p 8 (e.g., +1.8V).

With regard to the right-hand or out_p side of the level shifter 500: the PMOS FET M_(P7) is turned off because the negative output signal out_n at the gate of M_(P7) is at a logic high level (e.g., +3.05V); the PMOS FET M_(P6) is turned off as the assist_p signal at the gate of M_(P6) is at the non-overdrive voltage level of vddpx (e.g., +3.05V); the NMOS FETs M_(N10) and M_(N11) are turned on since the negative input voltage at the gate of M_(N11) is at a logic high level (e.g., +1.8V); the NMOS FET M_(N12) is turned on since the negative output voltage out_n at the gate of M_(N9) is at a logic high level vddpx (e.g., +3.05V); and the PMOS FET M_(P8) is turned off since the source and gate are both at vdd_1 p 8 (e.g., +1.8V).

At time t₁, the positive and negative input voltages V_(mp) and V_(mn) transition to logic high and low levels, respectively. In response to the negative transition of the negative input voltage V_(mn), the assist_p generator 550 and the V_(gp) generator 560 generate the assist_p and V_(gp) signals substantially coincidental at overdrive levels V_(ovd1p) and V_(ovd2n), respectively. The overdrive voltage levels for the assist_p and V_(gp) signals cause the PMOS FETs M_(P6) and M_(P8) to turn on. The turning on of the sixth PMOS FET M_(P6) applies vddpx to the out_p node to cause the positive output signal out_p to rise.

At time t₂, the positive and negative output voltages out_p and out_n has risen and fallen sufficiently to turn off the PMOS FET M_(P4) and turn on the PMOS FET M_(P7) turns on. At such time t₂, the assist_p generator 550 and Vgp generator 560 returns the assist_p and V_(gp) signals at the non-overdrive levels vddpx (e.g., +3.05V) and vdd_1 p 8 (e.g., +1.8V), respectively. At time t₃, the positive and negative output voltages out_p and out_n now being at logic high and low levels turn on and off the NMOS FETs M_(N9) and M_(N12), respectively. The NMOS FET M_(N9) being turned on applies vdd_1 p 8 to the out_n node; thus, the negative output voltage out_n becomes a logic low level at vdd_1 p 8. The NMOS M_(N12) being turned off while the PMOS M_(P7) being turned on applies vddpx to the out_p node; thus, the positive output voltage out_p becomes a logic high level at vddpx.

At time t₄, the positive and negative input voltages V_(mp) and V_(mn) transition to logic low and high levels, respectively. In response to the negative transition of the positive input voltage V_(mp), the assist_n generator 530 and the V_(gn) generator 540 generate the assist_n and V_(gn) signals substantially coincidental at overdrive levels V_(ovd1n) and V_(ovd2p), respectively. The overdrive voltage levels for the assist_n and V_(gn) signals cause the PMOS FETs M_(P3) and M_(P5) to turn on. The turning on of the PMOS FET M_(P3) applies vddpx to the out_n node to cause the negative output signal out_n to rise.

At time t₅, the positive and negative output voltages out_p and out_n has fallen and risen sufficiently to turn on the PMOS FET M_(P4) and turn off the PMOS FET M_(P7) turns on. At such time t₅, the assist_n generator 530 and V_(gn) generator 540 return the assist_n and V_(gn) signals at the non-overdrive levels vddpx (e.g., +3.05V) and vdd_1 p 8 (e.g., +1.8V), respectively. At time t₆, the positive and negative output voltages out_n and out_p have transitioned to logic high and low levels to turn on and off the NMOS FETs M_(N12) and M_(N9), respectively. The NMOS FET M_(N12) being turned on applies vdd_1 p 8 to the out_p node; thus, the positive output voltage out_p becomes a logic low level at vdd_1 p 8. The NMOS M_(N9) being turned off while the PMOS M_(P4) being turned on applies vddpx to the out_n node; thus, the negative output voltage out_n becomes a logic high level at vddpx.

FIG. 6 illustrates a schematic diagram of an exemplary assist_n generator 600 in accordance with another aspect of the disclosure. The assist_n generator 600 may be an exemplary detailed implementation of the assist_n generator 530 previously discussed.

The assist_n generator 600 includes a NOR gate 610, an inverter 620, a PMOS FET M_(P9), an NMOS FET M_(N13), and another NMOS FET M_(N14). A first input of the NOR gate 610 and an input of the inverter 620 is configured to receive the positive input signal V_(mp). The inverter 620 includes an output coupled to a second input of the NOR gate 610. The PMOS FET M_(P9), NMOS FET M_(N13), and NMOS FET M_(N14) are coupled in series in that order between the vddpx voltage rail and the GND voltage rail. A bias voltage V_(ssx) is applied to a gate of PMOS FET M_(P9). A bias voltage vdd_1 p 8 for over-voltage protection is applied to a gate of NMOS FET M_(N13). The NOR gate 610 includes an output coupled to a gate of the NMOS FET M_(N14). An assist_n signal is generated at a node between the PMOS FET M_(P9) and the NMOS FET M_(N13), which is substantially at vddpx when NMOS FET MN₁₄ is turned off.

The NOR gate 610 is configured to generate a pulse p_pulse in response to a negative transition of the positive input voltage Vmp. The width of the pulse p_pulse is determined by the delay of the inverter 620, which, unlike the width of the pulse enable signal V_(pulse_en) of I/O driver 200, is independent of the output voltage signal. The pulse p_pulse temporarily turns on the NMOS FET M_(N14). The turning on of NMOS FET M_(N14) lowers the assist_n voltage based on vddpx multiplied by a ratio of the sum of the turn-on resistances of the NMOS FETS M_(N13) and M_(N14) to the sum of the turn-on resistances of the PMOS FET M_(P9), NMOS FETs M_(N13) and M_(N14). Accordingly, in response to the negative transition of the positive input voltage V_(mp), the assist_n is lowered to the gate overdrive voltage V_(ovd1n), as previously discussed in detail in connection with level shifter 500.

FIG. 7 illustrates a schematic diagram of an exemplary assist_p generator 700 in accordance with another aspect of the disclosure. The assist_p generator 700 may be an exemplary detailed implementation of the assist_p generator 550 previously discussed.

The assist_p generator 700 includes a NOR gate 710, an inverter 720, a PMOS FET M_(P10), an NMOS FET M_(N15), and an NMOS FET M_(N16). A first input of the NOR gate 710 and an input of the inverter 720 is configured to receive the negative input signal V_(mn). The inverter 720 includes an output coupled to a second input of the NOR gate 710. The PMOS FET M_(P10), NMOS FET M_(N15), and NMOS FET M_(N16) are coupled in series in that order between the vddpx voltage rail and the GND voltage rail. A bias voltage V_(ssx) is applied to a gate of PMOS FET M_(P10). A bias voltage vdd_1 p 8 for over-voltage protection purpose is applied to a gate of NMOS FET M_(N15). The NOR gate 710 includes an output coupled to a gate of the NMOS FET M_(N16). An assist_p signal is generated at a node between the PMOS FET M_(P10) and the NMOS FET M_(N15), which is substantially at vddpx when NMOS FET MN₁₆ is turned off.

The NOR gate 710 is configured to generate a pulse n_pulse in response to a negative transition of the negative input voltage V_(mn). The width of the pulse n_pulse is determined by the delay of the inverter 720. The pulse n_pulse temporarily turns on the NMOS FET M_(N16). The turning on of NMOS FET M_(N16) lowers the assist_p voltage based on vddpx multiplied by a ratio of the sum of the turn-on resistances of the NMOS FETs M_(N15) and M_(N16) to the sum of the turn-on resistances of the PMOS FET M_(P10), NMOS FETS M_(N15) and M_(N16). Accordingly, in response to the negative transition of the negative input voltage V_(mn), the assist_p signal is lowered to the overdrive voltage V_(ovd1p), as previously discussed in detail in connection with level shifter 500.

FIG. 8 illustrates a schematic diagram of another exemplary V_(gn) generator 800 in accordance with another aspect of the disclosure. The V_(gn) generator 800 may be an exemplary detailed implementation of the V_(gn) generator 540 previously discussed.

The V_(gn) generator 800 includes a PMOS FET M_(P11) and an NMOS FET M_(N17) coupled in series in that order between the vddpx voltage rail and the GND voltage rail. A bias voltage V_(ssx) is applied to a gate of the PMOS FET M_(P11). The NMOS FET M_(N17) is configured to receive the p_pulse generated by the assist_n generator 600 previously discussed. The gate voltage V_(gn) is generated at a node between the PMOS FET M_(P11) and the NMOS FET M_(N17).

In operation, when the pulse p_pulse is not being generated and NMOS FET M_(N17) is turned off, the gate voltage V_(gn) is at substantially vddpx. When the pulse p_pulse is generated in response to a negative transition of the positive input voltage V_(mp), the NMOS FET M_(N17) turns on, and the gate voltage V_(gn) is lowered to vddpx multiplied by a ratio of the turn-on resistance of NMOS FET M_(N17) to the sum of the turn-on resistances of the PMOS M_(P11) and NMOS M_(N17). Accordingly, in response to the negative transition of the positive input voltage V_(mp), the gate voltage V_(gn) is lowered to the overdrive voltage V_(ovd2n), as previously discussed in detail in connection with level shifter 500.

FIG. 9 illustrates a schematic diagram of another exemplary V_(gp) generator 900 in accordance with another aspect of the disclosure. The V_(gp) generator 900 may be an exemplary detailed implementation of the V_(gp) generator 560 previously discussed.

The V_(gp) generator 900 includes a PMOS FET M_(P12) and an NMOS FET M_(N18) coupled in series in that order between the vddpx voltage rail and the GND voltage rail. A bias voltage V_(ssx) is applied to a gate of the PMOS FET M_(P12). The NMOS FET M_(N18) is configured to receive the n_pulse generated by the assist_p generator 700 previously discussed. The gate voltage V_(gp) is generated at a node between the PMOS FET M_(P12) and the NMOS FET M_(N18).

In operation, when the pulse n_pulse is not being generated and NMOS FET M_(N18) is turned off, the gate voltage V_(gp) is at substantially vddpx. When the pulse n_pulse is generated in response to a negative transition of the negative input voltage V_(mn), the NMOS FET M_(N18) turns on, and the gate voltage V_(gp) is lowered to vddpx multiplied by a ratio of the turn-on resistance of NMOS FET M_(N18) to the sum of the turn-on resistances of the PMOS M_(P12) and NMOS M_(N18). Accordingly, in response to the negative transition of the negative input voltage V_(mn), the gate voltage V_(gn) is lowered to the overdrive voltage V_(ovd2p), as previously discussed in detail in connection with level shifter 500.

FIG. 10 illustrates a flow diagram of an exemplary method 1000 of generating an output voltage signal based on an input voltage signal in accordance with another aspect of the disclosure.

The method 1000 includes applying a first gate voltage to a first gate of a first field effect transistor (FET) based on the input voltage signal (block 1010). Examples of means for applying a first gate voltage to a first gate of a first field effect transistor (FET) based on the input voltage signal include level shifter 220, level shifting component 410, assist_n generator 530, assist_p generator 550, assist_n generator 600, and assist_p generator 700.

The method 1000 further includes applying a second gate voltage to a second gate of a second (FET) based on the input voltage signal, wherein the first and second FETs are coupled in series between a first voltage rail and a second voltage rail, and wherein the output voltage signal is produced at an output node between the first and second FETs (block 1020). Example of means for applying a second gate voltage to a second gate of a second (FET) based on the input voltage signal includes buffer 230.

The method 1000 further comprises temporarily reducing the first gate voltage during a portion of a transition of the output voltage signal from a logic low level to a logic high level (block 1030). Examples of means for temporarily reducing the first gate voltage during a portion of a transition of the output voltage from a logic low level to a logic high level include overdrive enable circuits 250 and 300, level shifter 400, assist_n generators 530 and 600, assist_p generators 550 and 700, Vgn generators 540 and 800, and Vgp generators 560 and 900.

FIG. 11 illustrates a block diagram of an exemplary wireless device 1100 in accordance with another aspect of the disclosure. The I/O drivers and level shifters described herein may be used in wireless device applications.

For instance, the wireless device 1100 includes a digital signal processing core 1110 including an I/O driver with level shifter 1115, a user interface 1120, a radio frequency (RF) transmitter 1130, an RF receiver 1140, an antenna interface 1150 (e.g., a diplexer), and an antenna 1160. The I/O driver with level shifter 1115 may be configured similar to I/O driver 200 with the specific level shifter 500 serving as the level shifter 220 of I/O driver 200.

Based on signals exchanged between the digital signal processing core 1110 and the user interface 1120, the digital signal processing core 1110 employing the I/O driver and level shifter 1115 generates a transmit digital signal TX_(D). The RF transmitter 1130 generates a transmit RF signal TX_(RF) by converting the transmit digital signal TX_(D) into an analog signal, frequency upconverting the analog signal to generate an RF signal, and power amplifying the RF signal. The transmit RF signal TX_(RF) is sent to the antenna 1160 via the antenna interface 1150 for transmission to one or more other wireless devices via a wireless medium.

The RF receiver 1140 may receive a receive RF signal RX_(RF) from one or more other wireless devices via the antenna 1160 and the antenna interface 1150. The RF receiver 1140 generates a received digital signal RX_(D) by low noise amplifying the receive RF signal RX_(RF), frequency downconverting the amplified RF signal to generate a baseband analog signal, and converting the baseband analog signal into digital format. The digital signal processing core 1110 receives the receive digital signal RX_(D). The digital signal processing core 1110 may process the receive digital signal RX_(D) based on signals exchanged between the digital signal processing core 1110 and the user interface 1120.

The previous description of the disclosure is provided to enable any person skilled in the art to make or use the disclosure. Various modifications to the disclosure will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other variations without departing from the spirit or scope of the disclosure. Thus, the disclosure is not intended to be limited to the examples described herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein. 

What is claimed:
 1. An apparatus, comprising: a first field effect transistor (FET) including a first gate coupled to a signal input; a second FET including a second gate coupled to the signal input, wherein the first and second FETs are coupled in series between a first voltage rail and a second voltage rail, and wherein a signal output is coupled between the first and second FETs; a third FET coupled between the first FET and the signal output, wherein the third FET includes a third gate; and a control circuit including an output coupled to the first and third gates of the first and third FETs, respectively, wherein the control circuit includes a first input coupled to the signal output.
 2. The apparatus of claim 1, wherein the control circuit includes a second input coupled to the second gate of the second FET.
 3. The apparatus of claim 1, wherein the control circuit comprises: a fourth FET including a gate coupled to the signal output and a source coupled to a third voltage rail; a fifth FET including a drain coupled to the signal output and a gate coupled to the third voltage rail; and a NOR gate including a first input coupled to a drain of the fourth FET and a source of the fifth FET, a second input coupled to the second gate of the second FET, and an output serving as the output of the control circuit.
 4. The apparatus of claim 3, wherein the NOR gate is coupled to the second and third voltage rails.
 5. The apparatus of claim 1, further comprising a first level shifter including a first input coupled to the signal input, a second input coupled to the output of the control circuit, and an output coupled to the first gate of the first FET.
 6. The apparatus of claim 5, wherein the first level shifter comprises: a level shifting component including input and output serving as the first input and output of the first level shifter; a resistor; a fourth FET including a fourth gate coupled to a third voltage rail; and a fifth FET including a fifth gate serving as the second input of the first level shifter, wherein the resistor, fourth FET and fifth FET are coupled in series between the output of the level shifting component and the second voltage rail.
 7. The apparatus of claim 5, further comprising a second level shifter including an input serving as the signal input, and an output coupled to the first input of the first level shifter and the second gate of the second FET.
 8. The apparatus of claim 7, wherein: the first level shifter is coupled to the first voltage rail, the second voltage rail, and a third voltage rail; and the second level shifter is coupled to the second voltage rail, the third voltage rail, and a fourth voltage rail.
 9. The apparatus of claim 7, further comprising a buffer including an input coupled to the output of the second level shifter, and an output coupled to the second gate of the second FET.
 10. The apparatus of claim 9, wherein the buffer is coupled to the second and third voltage rails.
 11. The apparatus of claim 1, further comprising an inverter including an input coupled to the output of the control circuit, and an output coupled to the third gate of the third FET.
 12. The apparatus of claim 1, further comprising a fourth FET coupled between the signal output and the second FET, wherein the fourth FET includes a fourth gate to receive a substantially constant bias voltage.
 13. A wireless device, comprising: an input/output (I/O) driver, comprising: a first field effect transistor (FET) including a first gate coupled to a signal input; a second FET including a second gate coupled to the signal input, wherein the first and second FETs are coupled in series between a first voltage rail and a second voltage rail, and wherein a signal output is coupled between the first and second FETs; a third FET coupled between the first FET and the signal output, wherein the third FET includes a third gate; and a control circuit including an output coupled to the first and third gates of the first and third FETs, respectively; a transmitter including an input coupled to the signal output of the I/O driver; and an antenna coupled to an output of the transmitter.
 14. The wireless device of claim 13, wherein the control circuit includes an input coupled to the signal output.
 15. The wireless device of claim 13, wherein the control circuit includes an input coupled to the second gate of the second FET.
 16. The wireless device of claim 13, wherein the I/O driver further comprises a level shifter including a first input coupled to the signal input, a second input coupled to the output of the control circuit, and an output coupled to the first gate of the first FET.
 17. The wireless device of claim 13, wherein the I/O driver further comprises an inverter including an input coupled to the output of the control circuit, and an output coupled to the third gate of the third FET.
 18. The wireless device of claim 13, wherein the I/O driver further comprises a fourth FET coupled between the signal output and the second FET, wherein the fourth FET includes a fourth gate to receive a substantially constant bias voltage. 